Efficacy and potency of class I antiarrhythmic drugs for suppression of Ca2+ waves in permeabilized myocytes lacking calsequestrin

Abstract

Background Ca2+ waves can trigger ventricular arrhythmias such as catecholaminergic-polymorphic ventricular tachycardia (CPVT). Drugs that prevent Ca2+ waves may have antiarrhythmic properties. Here, we use permeabilized ventricular myocytes from a CPVT mouse model lacking calsequestrin (casq2) to screen all clinically available class I antiarrhythmic drugs and selected other antiarrhythmic agents for activity against Ca2+ waves. Methods and Results Casq2−/− myocytes were imaged in line-scan mode and the following Ca2+ wave parameters analyzed: wave incidence, amplitude, frequency, and propagation speed. IC50 (potency) and maximum inhibition (efficacy) were calculated for each drug. Drugs fell into 3 distinct categories. Category 1 drugs (flecainide, R-propafenone) suppressed wave parameters with the highest potency (IC50 < 10 μM) and efficacy (> 50% maximum wave inhibition). Category 2 drugs (encainide, quinidine, lidocaine, verapamil) had intermediate potency (IC50 20 μ 40 μM) and efficacy (20% - 40% maximum wave inhibition). Category 3 drugs (procainamide, disopyramide, mexilitine, cibenzoline, ranolazine) had no significant effects on Ca2+ waves at the highest concentration tested (100 μM). Propafenone was stereoselective, with R-propafenone suppressing waves more potently than S-propafenone (IC50: R-propafenone 2±0.2 μM vs. S-propafenone 54±18 μM). Both flecainide and R-propafenone decreased Ca2+ spark mass and converted propagated Ca2+ waves into non-propagated wavelets and frequent sparks, suggesting that reduction in spark mass, not spark frequency, was responsible for wave suppression. Conclusions Among all class I antiarrhythmic drugs, flecainide and R-propafenone inhibit Ca2+ waves with the highest potency and efficacy. Permeabilized casq2−/− myocytes are a simple in-vitro assay for finding drugs with activity against Ca2+ waves.

Mechanism of Antiarrhythmic Effects of Flecainide in Catecholaminergic Polymorphic Ventricular Tachycardia

“…4 One of the points of difference between the data of Liu et al and our work is the effect of flecainide on sarcoplasmic reticulum Ca 2ϩ sparks: no apparent effect in RyR2 R4496Cϩ/Ϫ cells in the study by Liu et al 1 and an increase in Ca 2ϩ spark frequency and reduction of spark amplitude, width, and overall spark mass in mouse and rat myocytes in our studies. 5,6 The discrepancy may relate to experimental conditions, because the basal Ca 2ϩ spark frequency in the experiments by Liu et al is several fold higher than that of our experiments. 1,5 If Ca 2ϩ spark frequency is already very high, it may be difficult to detect any further increases caused by flecainide.…”

The Direct Actions of Flecainide on the Human Cardiac Ryanodine Receptor

“…The article provided evidence that in the case of CPVT, its antiarrhythmic action was not via inhibition of I Na , but instead via inhibition of the activity of the cardiac ryanodine receptor (RyR2) and subsequent reduction in the proarrhythmic release of Ca 2+ during diastole. This interpretation was supported by further work by the Knollman and his collaborators, 2,3 in particular, the demonstration of direct effects of flecainide and the related more potent local anesthetic R-propafenone 3 on SR Ca 2+ release in permeabilized cardiac muscle preparations. However, the interpretation of this result is controversial.…”

Ca2+ Sparks and Ca2+ waves are the subcellular events underlying Ca2+ overload during ischemia and reperfusion in perfused intact hearts

“…Data supporting this last statement are presented in Fig 4E–G, where the spatial profile and velocities are shown for both, the preischemic and the ischemic conditions. In contrast, common events observed in association with the frequent Ca 2+ sparks during ischemia are non-propagated mini-waves or wavelets, similar to those observed with antiarrhythmic agents like flecainide and R-propafenone that act by reducing RyR2 inhibition [29,30]. …”